Abstract: In the old extension transformation reasoning, extension transformation used historical infom}ation or personal experience, which restricted its application in intclligentized rcaso-ning. For solving the problem, an extension reasoning method based on rough set data analysis was proposed. The method gained some classified and rule knowledge by analyzing data with rough set firstly, then used the information to guide extension reasoning, which will make extension transformation reasoning become easy control and good efficiency and lay a foundation for its application in intelligentized reasoning.

Key words: Extension reasoning, Rough set, Data analysis